Battery light on and low voltage

[dogren]

Truck is bone stock '01, 202,000 miles. Has red tops that are a few years old. Checked both while disconnected and both read 12.35 volts. Have not load tested batteries or alternator. Since the volt gage stayed low after the GP/air heater cycle, thought the GP/air heater controller/relay was bad. Replaced the GP/air heater contoller/relay and still have the problem. The truck cranks/starts/runs fine. The battery symbol stays on in the message center and the volts read low (10-11) constant - they don't kick up after the GP/heater cycle. The alternator, GP's and air heater are original. Need help. Can the truck be driven to load test the batteries and alternator? Could this be a stuck relay somewhere else? GP failure? Or just a bad alternator?
Thanks in advance,
Dave

[rapidoxidationman]

Put a volt meter on the batteries, note the voltage.
Start the truck, note the voltage.
Add loads to the electrical system, noting the voltage with each additional load (wipers, headlights, blower motor, cigarette lighter, blah blah blah

I'll bet you see lower and lower numbers with each additional load and that you'll find it is time for a new alternator.

[DmaxMaverick]

As quickrustdude said, check your voltage before/after a start, and note the voltages with the addition of accessories. If the voltage drops (or never comes up), it's most likely the alternator.

Get your new one HERE (http://alternatorparts.com/), OEM or upgrade. Best place I've found. Ever! All new components, and made in the USA. 1/2 the price (or less) of the dealer. I've bought from him several times, and haven't been disappointed. He answers his own phone.

[dogren]

Thanks guys. Can the truck be driven approx. 15 miles? Since I'm not where the truck is right now I may need to have my son look into this for me. And is this a simple swap like the GP/air heater contoller/relay was? We are really green...
Thanks in advance,
Dave

[DmaxMaverick]

Driving isn't a problem, as long as the (otherwise healthy) batteries are well charged. It won't hurt anything or leave you stranded unless the voltage gets too low (10V or less). Don't rely on the IPC gage for actual system voltage. The gage indicates perceived system voltage, and is effected by most current loads on the system at the time (creating a superficial low indication). With a full battery charge, you can drive a long way, and it depends mostly on the accessories/lighting you use. Avoid driving with the headlamps on, or using the HVAC blower (roll down the windows instead of using the A/C). In most cases, driving during the day doesn't use much power. Night driving will, obviously, use more. Leave off the bumpin' sound and/or entertainment systems, too. 15 miles is relatively very little usage, in any case.

Replacement is remarkably simple. Remove the belt, unplug/unbolt the connectors at the alternator, remove 2 bolts, and lift away. Replace in reverse order (use anti-seize on the bolt threads and clean mating surfaces). At 200K+ miles, I also suggest replacing the tensioner and idler pulley(ies), and the belt.

[dogren]

Thank you good sir. Your input is very much appreciated.
Dave

[DmaxMaverick]

Previous post corrected. There are 2 bolts, not 4. Got my jobs mixed up.

Anyway, R/R may require a little persuasion with the bolt-throughs. Careful prying on them, as they are cast aluminum (no warning, they just snap). The bolt holes on the alternator have steel bushing inserts (or should have), and they can be adjusted. They should be very tight, but not to the point they shave the mounts going in. Most go in easy, but some are very tight. You can use a soft punch/mallet (brass and dead-blow) on the mounting tabs for a bit of fine adjustment to get the bolts started (once they start, it will self-align), but avoid hitting the housing or shaft/pulley.